1. Field of the Invention
The present invention relates to a combustion chamber for a diesel engine, and more particularly to the configuration of a combustion chamber for reducing the creation of noxious components in the exhaust gas.
2. Discussion of Background
Conventionally, the structure is known for a combustion chamber of a diesel engine wherein the combustion chamber is provided as a concave section in the head surface of a piston and fuel is injected directly into the air which is compressed in this combustion chamber. This type of combustion chamber is referred to as a toroidal combustion chamber.
When the piston rises, the air inside the combustion chamber is caused to rotate to produce an eddying flow. Then, in order for the flow of fuel to intersect this eddying flow and be accelerated, the eddying flow must have the strength to rotate over the entire periphery so that the fuel is uniformly mixed in the circumferential direction, in the interval between consecutive injections.
In addition, the mixture of fuel and air is made uniform, and, in particular, there is no temporary concentration of fuel. Therefore, because the fuel is injected continuously, there is an effective reduction of black smoke and NO.sub.x which are noxious substances in the exhaust gases.
For these reasons, conventionally, it has been proposed that the shape of the concave section in the combustion chamber be made heart-shaped, or hemispherical or globular.
However, with a combustion chamber of any of the abovementioned shapes, the combustion at the side wall surface, where the best mixing of the fuel and air is considered to occur, is not complete, and there is a tendency for incomplete combustion to be obtained.
Specifically, the fuel which is injected into the center of the combustion chamber is not sufficiently dispersed and is not broken down into fine particles. It is therefore not in a state in which ignition can occur from contact with the air. As a result, the air at the center of the eddying flow does not particularly contribute to the effect of smooth ignition of the fuel. The mixture of the fuel and air close to the surface of the side wall is vigorously mixed, but there is a tendency toward a lack of air which is necessary for combustion. Therefore, when sufficient air to burn the fuel is lacking, incomplete combustion occurs and there is a large amount of noxious components produced in the exhaust gases.
In addition, because the mixing and agitation of the air and fuel at the concave section of the side wall surface depends on the strength of the eddying flow, it is difficult to guarantee a uniform mixing performance.